1. Field of the Invention
The present invention relates to a metal bending apparatus, and more specifically an apparatus and method for bending a heat exchanger coil comprised of a plurality of tubes with plate-like fins carried thereon.
2. Description of the Prior Art
Heat exchanger coils are generally composed of a plurality of tubes which preferably carry fins to increase the surface area and to thereby increase the efficiency of the heat exchange provided by the tubes between a fluid flowing within the tubes and a fluid flowing around the outside of the tubes. Generally, the tubes are originally formed in a linear fashion and the fins are attached to the tubes while the tubes are in such a linear state. Subsequently, it is often desirable to provide one or more bends in the tubes in order to shape the coil to various assembled environments, for example, the coil may have one or more right angle bends to generally form a rectangular perimeter in an assembled condition.
A number of methods and apparatus for bending coils and, in particular, heat exchanger coils with fins, have been proposed in prior art. For example, U.S. Pat. No. 3,443,296 discloses a coil bender that clamps the coil in two places and applies a bending motion that decreases in radius over the entire bend.
U.S. Pat. No. 3,785,190 discloses a tube bender having a spindle 12 around which the tube is deformed, and a linear clamp shoe 30 which moves with the tube during the bend.
U.S. Pat. No. 3,958,440 discloses a die block that is laterally retractable to an inoperative position between bends and U.S. Pat. No. 2,667,202 discloses a clamping die 43 which moves synchronously with a die wheel 24 and stop 74 to restrain a portion of the tube during the bend.
Problems develop during the bending of a coil, especially when fins are carried on the tubes in that pressure tends to build up on the inside bend radius which can cause the fins to deform during the bending process since the bend normally occurs around a mandrel. This deformation of fins is more pronounced in fins having enhancements formed in the surfaces, which tend to weaken the fin.